Process for producing three-dimensional structure

ABSTRACT

A process for producing a periodic structure comprises the steps of preparing a working object, the property of which changes in view of a photoreaction caused by an exciting energy, generating a light having a photonic energy of intensity of one fraction of natural number divisions of the exciting energy by each of the light sources of light-source groups arranged regularly in a two-dimensional arrangement, and concentrating the light emitted from the light source group at each of the light-concentrating points arranged at regular intervals in the working object to cause a photoreaction at and around the light-concentrating point to form a periodic structure comprised of regions each of which has a changed property in the working object.

TECHNICAL FIELD

The present invention relates to a process for producing athree-dimensional structure, in particular to a process for producing athree-dimensional photonic crystal.

BACKGROUND ART

Recently, fine processing techniques and fine processing apparatuseshave been developed for processing at a level that is finer than thevisible light wavelength, such as those in semiconductor processingtechniques. Further, techniques and apparatuses for working of opticalelements having a structure on a light wavelength level have beendeveloped, such as photonic crystals different from electronic elements.In particular, in the field of optical elements, a process for producinga two-dimensional air-bridge type photonic crystal is disclosed, whichprocess employs electron-beam lithography and reactive-ion-beam etching(Physical Review Letters, vol. 86, No. 11, p. 2289). Further, a processfor producing a three-dimensional photonic crystal is disclosed, inwhich the three-dimensional photonic crystal is produced by laminatingdifferent substances alternately by auto-cloning on a two-dimensionalperiodic structure formed on a substrate (Applied Physics Letter, vol.77, No. 26, p. 4256). Further, a process for producing athree-dimensional photonic crystal is disclosed, in which fine Sispheres are arranged in a solvent (Nature, vol. 414, p. 289).

Although structures having a desired two-dimensional configuration canbe produced by a semiconductor processing technique, the processing inthe height direction is conducted by a lamination technique, so that athree-dimensional fine periodic structure cannot readily be produced.Further, in the aforementioned process of lamination of differentsubstances on a two-dimensional periodic structure formed on asubstrate, there are difficulties associated with the necessity tomaintain strict cleanliness and flatness of the substrate forprocessing, a lengthy amount of time required for lamination, the needfor labor to exchange the laminating substance, and the need forconducting evacuation for film formation. In the process of arrangementof styrene spheres in a solvent, there are problems associated with thenecessity to maintain the flatness of the substrate, to control thetemperature and the humidity of the preparation atmosphere, and that atime period of days or months is required for the arrangement formation.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided aprocess for producing a periodic structure, comprising the steps of:

preparing a working object, a property of which is changed by aphotoreaction caused by an exciting energy;

generating a light having a photonic energy of intensity of one fractionof natural number divisions of the exciting energy by each of the lightsources of light-source groups arranged regularly in a two-dimensionalarrangement; and

concentrating the light emitted from the light source group at each oflight-concentrating points arranged at regular intervals in the workingobject to cause the photoreaction at and around the light-concentratingpoint to form a periodic structure comprising regions, each of which hasa changed property in the working object.

The photoreaction is preferably a multiphoton absorption reaction.

The lights from the light source group to the working object arepreferably introduced through a light-condensing optical system.

The lights from the light source group are preferably coherent lights,and are preferably interfere with each other in the working object tomake the lights concentrated.

The lights from the light source group are preferably generated by asingle light-generating source.

The light source group is preferably comprised of a singlelight-generating source and a mask having fine pores arrangedperiodically in one plane, and the light from the light-generatingsource is preferably introduced to one face of the mask and emitted fromthe other face thereof.

The light source group is preferably comprised of a singlelight-generating source and a microlens array comprising microlensesarranged periodically in one plane, and the light from thelight-generating source is preferably introduced to one face of themicrolens array and emitted from the other face thereof.

The light source group is preferably comprised of a singlelight-generating source and an optical fiber bundle of regularly bundledoptical fibers, where each fiber has a microlens on one end. The lightfrom the light-generating source is preferably introduced to an end ofthe optical fiber bundle without the microlens and is emitted from theother end of the fiber bundle.

The periodic structure is preferably formed in three dimensions bychanging the relative position of the concentrated points and theworking object.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the apparatus for producing a fine periodicalstructure of Example 1 of the present invention.

FIG. 2 illustrates the drive-controlling device employed in theapparatus for producing a fine periodical structure of Example 1 of thepresent invention.

FIG. 3 illustrates the optical fiber employed in the apparatus forproducing a fine periodical structure of Example 2 of the presentinvention.

FIG. 4 illustrates the optical fiber bundle employed in the apparatusfor producing a fine periodical structure of Example 2 of the presentinvention.

FIG. 5 illustrates the arrangement in the optical fiber bundle employedin the apparatus for producing a fine periodical structure of Example 2of the present invention.

FIG. 6 illustrates the apparatus for producing a fine periodicalstructure of Example 2 of the present invention.

FIG. 7 illustrates the mask employed in Example 3 of the presentinvention.

FIG. 8 illustrates the mask employed in Example 3 of the presentinvention.

FIG. 9 illustrates generation of divergent light beams by the mask inExample 3.

FIG. 10 illustrates the apparatus for producing a fine periodicalstructure of Example 3 of the present invention.

FIG. 11 illustrates introduction of light into the optical fiber bundlein Example 4 of the present invention.

FIG. 12 illustrates the apparatus for producing a fine periodicalstructure of Example 4 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

When irradiated with a light beam, a photosetting resin or a resist,such as an epoxy resin and a urethane-acrylate resin, undergoes or doesnot undergo a curing reaction locally corresponding to the distributionof the light intensity of the projected light. In a photosetting resin,the portion irradiated with light of an intensity higher than thethreshold of the reaction reacts to become cured, whereas the portionirradiated with the light of a lower intensity is not cured and remainsin the liquid state. Removal of the uncured liquid-state resin bywashing leaves a cured resin portion constituted of a fine periodicstructure having a refractive index period of an order of a lightwavelength, namely on the order several hundred nanometers. The workingobject to be processed in the present invention comprises a substancethe property of which, such as the refractive index, changes in view ofthe absorption of the optical energy sufficient for causing a reactionfor the change to occur, namely a threshold energy or more (hereinafter,the necessary threshold energy is referred to simply as an “excitingenergy”).

The terms in the present invention are defined as below:

“Unit light” is a light, which is emitted from each of the light sourcesconstituting one of the light source groups arranged in atwo-dimensional regular period, and has the photonic energy of one of Nfractions (N: a natural number, hereinafter referred to as “1/N-photonicenergy”) of the above-defined exciting energy.

“Unit light source” is a source, which emits the unit light.

“Unit light group” is a group of the unit lights and has the excitingenergy as a whole. “Unit light source group” is a group of the unitlight sources, which emit a unit light group as a whole. The unit lightsource group is therefore implied by the above-mentioned light sourcegroup arranged in a two-dimensional regular period.

“Light-concentrating point” is a point where the unit lights consistingof the unit light group are focused in the working object.

“Exciting light” is a unit light group concentrated at onelight-concentrating point and having the exciting energy.

“Unit light-concentrating means” is a means for concentrating the unitlights consisting of the unit light group at one light-concentratingpoint into the exciting light.

“Exciting light-generating means” is a combination of the unit lightsource group and the unit light-concentrating means.

The present invention is practiced as described below.

The exciting light-generating means and a working object are placed soas to bring the light-concentrating point at a prescribed position inthe working object, and lights of the unit light group are introducedinto the working object. The exciting light causes a reaction in aregion at and around the light-concentrating point to change theproperty in the region. For example, plural parallel laser beamsemployed as the unit light group are introduced through a convex lens asthe unit light-concentrating means into the working object to be focusedat the focal point of the convex lens. Thereby, a reaction is caused atand around the focal point. The focused light, which is capable ofcausing a reaction, may be the exciting light, and the focal point maybe the light-concentrating point of the present invention.

In the present invention, “convergent light” signifies the light, whichhas the cross-sectional area of the projected light at the planevertical to the light propagation direction (hereinafter referred to asan “optical axis”), decreases gradually along the light propagationdirection to a minimum at a certain point and then increases graduallywith the light propagation. An example is a parallel light beamconverged by passage through a convex lens. In the present invention,the term “convergent light” signifies the light before focusing at thelight-concentrating point. A group of the convergent light emitted fromplural unit light groups is called a “convergent light group”. Whenparallel light is converged and introduced into an object, and causes aphotoreaction at the center of the minimized area of the convergedlight, the center is the light-concentrating point in the presentinvention.

On the other hand, in the present invention, “divergent light” signifiesthe light, which has the cross-sectional area of the projected light atthe plane vertical to the optical axis, increases gradually along thelight propagation direction. Examples are parallel light beams afterpassage through a concave lens; parallel light beams diverging afterfocusing by a convex lens; and light emitted from a point light source.When two coherent divergent lights are superposed spatially, thedivergent lights interfere with each other to result in a periodicdistribution of the light intensity. If each of the lights at anti-nodesof the interference fringe has an intensity equal to or higher than theexciting energy, then the light may be the exciting light in the presentinvention, and a portion at which the antinode exists may be thelight-concentrating point of the present invention. The light is calledthe “anti-node light” in the context of the present invention.

The regular arrangement of the light-concentrating points within theworking object is called a “light-concentrating point array”. A fineperiodic structure having a two-dimensional regular period can be formedat an intended position in a working object by driving the excitinglight-generating means and/or the working object in a controlled mannerso as to bring the light-concentrating point array to the intendedposition in the working object. For example, the controlled-drivingmeans moves a working object supported by a piezo element or the likeand by driving the piezo element electrically with the other partsfixed.

In the present invention, the term “a unit-light source group array”signifies an array of the unit light source groups serving as the lightsource of the array of the unit light groups focusing on thelight-concentrating point array.

The term “an exciting light array” signifies an array of the excitinglight at the light-concentrating point array.

The term “a unit light-concentrating means array” signifies an array ofthe means for concentrating the light emitted from the unit light sourcegroup array to form the exciting light array.

The combination of the unit-light source group array and the unitlight-concentrating means array constitutes an “exciting lightarray-forming means”.

The exciting light array-forming means enables formation of thelight-concentrating point array in one step. In an embodiment of thepresent invention, a fine periodic structure is produced byconcentrating an array of the unit light groups emitted from aunit-light source group array through a unit light-concentrating meansarray on a light-concentrating point array to cause a photoreaction bythe formed exciting light array.

In the case where the unit-light group is passed through a unitlight-concentrating means and the transmitted light is convergent, therespective terms of a unit-light group, exciting light, a unitlight-concentrating means, an exciting light-generating means, aunit-light source group array, an exciting light array, a unitlight-concentrating means array, and an exciting light array-formingmeans are referred to respectively as “a convergent-light source”,“focused light”, “a light-converging means”, “a focused light-generatingmeans”, “convergent light source array”, “a focused light array”, “aconverging means array”, and “a focused light array-forming means”.

On the other hand, in the case where the unit-light group is constitutedof at least one of divergent coherent lights, the respective terms of aunit-light group, exciting light, a unit light-concentrating means, anexciting light-generating means, a unit-light source group array, anexciting light array, a unit light-concentrating means array, and anexciting light array-forming means are referred to respectively as “adivergent-light source”, “antinode light”, “a light-diverging means”, “adivergent light generating means”, “divergent light source array”, “anantinode light pattern”, “a diverging means array”, and “a divergentlight array-forming means”.

In the case where the unit-light group is passed through a unitlight-concentrating means and the transmitted light is convergent, inone embodiment of the present invention, a fine periodic structure isproduced by converging the light beams from convergent-light sourcesthrough a light-converging means array and focusing the converged lighton a focus point array as the light-concentrating point array to cause aphotoreaction by the obtained focused light array.

In another embodiment of the present invention, a working object isprocessed by introducing thereto divergent coherent light. In thisembodiment, a divergent-light source array and a diverging means arrayare arranged to bring an antinode light pattern to the intended positionin the working object, and plural divergent lights are introducedthrough the diverging means array into the working object to generatethe antinode light pattern. Thereby, a reaction is caused at and aroundthe respective antinode centers to form an array of the regions havingthe changed property corresponding to the pattern. The antinode lightpattern gives a larger number of light-concentrating points from thesame number of unit-light sources than the focused light array,producing a fine periodic structure more efficiently.

A three-dimensional fine periodic structure can be prepared in a workingobject through the following steps: forming an exciting light array byuse of an exciting light array forming means to cause a photoreaction asa first processing step, and conducting, after shifting the relativeposition of the working object and the light-concentrating point array,a second processing step in the same manner as the first process step;or conducting the processing with continuous shifting of the relativeposition of the working object to the light-concentrating point array inthe working object. In the present invention, the process for obtaininga fine three-dimensional periodic structure in which the relativeposition of the exciting light array forming means of the presentinvention and the working object is shifted during the processing issimply called “a three-dimensional process”.

One unit light having an energy of 1/N-photonic energy equal to theexciting energy (i.e., N=1) is capable of causing a reaction at alight-projected small region in the working object by itself as anexciting light without combining another unit light into a unit-lightgroup, so that the unit light is capable of conducting fine processinglocally with the aid of a simply structured exciting light-generatingmeans consisting of a source of the unit light not constituting anyunit-light source group and a unit light-concentrating meanscorresponding to the source. For example, in the case where aconvergent-light source consists of a single unit-light source, theconvergent light from the unit-light source can be considered as theunit light having the exciting energy on the basis of the definitions ofthe terms, and is therefore capable of causing the reactions as thefocused light by itself. Thereby, the fine processing as mentioned abovecan be conducted in the interior of the working object, provided thatthe fine controlled driving of such a simply structured focused lightgenerating means consisting of the focused-light source and the focusingmeans can be conducted.

A working object to be processed by a high-order nonlinear opticalprocess, such as a two-photon process, requires a much higher energy inthe working object for a remarkable result. For example, in a workingobject requiring twice the exciting energy for a one-photon processthrough the entire process, the irradiation of a unit-light groupconstituted of N unit light beams each having the 1/N-photonic energy,which is useful in a one-photon process, will not cause the reaction. Inthis working object, the reaction is caused by receiving twice theenergy in total. In other word, by the two-photon process, the reactioncan be caused in a range smaller than that of the light-concentratingpoint area where the reaction is caused by a one-photon photoreaction.This enables finer local processing of the working object.

The apparatus for producing the fine periodic structure of the presentinvention may be equipped with a temperature-control mechanism forcontrolling the temperature of the working object before, during, andafter the processing. By controlling the temperature of the workingobject by the temperature-controlling mechanism, the processing can beconducted with high precision without the influence of the environmentalconditions, such as temperature.

As described above, not only a two-dimensional structure, but athree-dimensional fine periodic structure constituted of plural unitshaving a unit size of tens to hundreds of nanometers can be produced bya simple constitution of the apparatus in a short period of time with alesser amount of labor involved. More precise processing can be achievedby utilizing a multiphoton process.

The embodiments of the present invention are described below.

Formation of Light Source Group by Mask

The unit-light source group may be formed from a single light source anda mask having fine pores arranged periodically on one plane. The lightprojected onto the one face of the mask passes through the fine pores ofthe mask and is emitted from the pores on the reverse face as pluraldivergent lights. The emitted plural divergent lights are passed througha convex lens for conversion into parallel lights, namely a unit-lightgroup, and the unit-light group is converged by passing through a secondconvex lens into an exciting light (the optical system comprised of suchtwo convex lenses for converging the divergent light is called “aconverging system”). One of the advantages of this embodiment is thatthe unit-light source group array can be formed from a smaller number oflight sources than the number of the unit-light groups, for example, asingle light source.

The spatial distribution of the convergent light or divergent light canbe controlled, or the pattern of the light-concentrating point array orthe light intensity distribution at a light-concentrating point can becontrolled by designing the arrangement pattern of the diameter or theintervals of the fine pores of the mask, or by making them variable.This facilitates the processing and production of the fine structurewith a high freedom degree. The mask having a variable size of the porescan be produced from a material stretchable by temperature, a materialstretchable by electricity, such as by a piezo element, or the like.

This embodiment having unit-light source group array having a lightsource and a mask has a simplified constitution of the exciting lightgenerating means or the exciting light array generating means. By thisembodiment, the three-dimensional process is facilitated. Theconstitution can be simplified further by using a convex lens in theconverging system, which has a size for covering the pattern of themask.

The unit-light source group may be constituted without employing theconverging system to form a light-concentrating point array by theinterference of plural divergent lights emitted from the fine pores.

Light Source Group with Lens Array

The exciting light array-forming means of the present invention may be afocused-light array-forming means constituted of a light source and afine lens array module having fine lenses arranged periodically.Examples of the fine lens array module include a microlens array modulecomprised of microlenses fixed by a resin by use of a mold and a finespherical lens array module comprised of microspherical lenses arrangedon a glass substrate. The lens array serves as the converging meansarray. The light from a light source projected onto one face of the finelens array module passes through the microlenses and is emitted from thefine pores on the other face as convergent lights to be focused at thelight-concentrating points inside the working object. Since themicrolenses are arranged two-dimensionally at regular intervals, thelight-concentrating points are also arranged two-dimensionally andperiodically to form a light-concentrating point array. The focusedlight array-forming means and/or the working object are driven in acontrolled manner to bring the light-concentrating point array to aprescribed position in the working object, whereby a fine periodicstructure can be produced at the prescribed positions in one step insidethe working object. This simple and durable structure facilitates thepositioning by driving a focusing light array forming means in thethree-dimensional process.

Light Source Group with Optical Fiber

A focused-light array-forming means is constructed from a light source.An optical fiber bundle is constituted of optical fibers bundledregularly and having a micro convex lens at one end of the respectiveoptical fibers. The micro convex lenses are arranged regularly at theend of the fiber bundle. The positions and intervals of thelight-concentrating points inside the working object can be controlledby the regularity of the arrangement. In an example of the optical fiberarrangement, an optical fiber bundle is constituted from six opticalfibers having a micro convex lens with the same diameter as the opticalfiber at one end of the respective fibers and another optical fiber withthe same diameter, but having no micro convex lens surrounded by theabove six optical fibers, and the peripheries of all of the micro convexlenses are in contact with the end of the central fiber. A light, suchas parallel light of a laser beam introduced to the ends of the opticalfibers having no micro convex lens, is emitted as convergent light fromthe micro convex lenses at the opposite ends. The emitted convergentlight is focused respectively in the working object to form alight-concentrating point array corresponding to the micro lens array.The use of optical fiber bundle as the exciting array-forming meanssimplifies the constitution. Further, the mechanical flexibility of theoptical fiber provides a higher degree of freedom in positioning of thelight-concentrating point array. When the light beams focused on thelight-concentrating points have respectively the exciting energy, thelight-concentrating points are the exciting light spot in the presentinvention, and the array of the light beams is a focused light array. Inthis case, the light transmitted through one of the optical fibershaving a micro convex lens has an exciting energy. Thus, by arrangingoptical fibers for transmitting a unit light group composed of one ormore unit light beams, a focused-light array-forming means can beconstituted readily without employing a complicated unitlight-concentrating means unit light-concentrating means array to obtainan intended light-concentrating point array.

As described above, the converging system, the fine lens array moduleand the micro convex lenses generate convergent lights, respectively.Here, a term “light-condensing optical system” means a lens or lensgroup, which generates convergent lights, such as the converging system,the fine lens array module and the micro convex lenses. Microlens arraymodule 102 and microlens 303 in Examples 1 and 2 described later,respectively, exemplify the light-condensing optical system. Alight-condensing optical system therefore may be comprised in a unitlight-concentrating means or a light-concentrating means array.

The light introduced to the optical fiber having no micro convex lens atone end is emitted from the other end of the fiber as divergent light.With a micro convex lens having a short focal length, the light isconverged and focused once and is then allowed to propagate as divergentlight. Therefore, the emitted divergent light can be controlled byselecting the focal length of the micro lenses. In this manner, adivergent light group can be generated from the optical fiber bundle.Therefore, in this embodiment, the light-concentrating point array canbe an array constituted of focused lights and can also be constituted ofan antinode light pattern. Thus, by utilizing the aforementionedadvantage of the focused light array-forming means comprised of thefiber bundle, the position, density and the like of the antinode lightpattern can be controlled.

Fine periodic structures having different basic patterns oflight-concentrating point arrays can readily be produced by providing anoptical switch for at least one fiber of the optical fiber bundle. Forexample, in the case where an optical fiber bundle is constituted suchthat the centers of the three microlenses are arranged in a triangularlattice two-dimensionally, and an optical switch is provided for each ofthe optical fibers, the arrangement of the light-concentrating pointscan be selected from one point, two points in different directions, andthree points in the triangle. The optical switch is exemplified by an AO(acousto-optic) element.

EXAMPLES

Specific examples of the present invention are discussed below withreference to the drawings. Throughout the drawings, the correspondingmembers are indicated by the same symbols.

Example 1

FIG. 1 shows a constitution of an apparatus for producing a fineperiodic structure employed in the present invention. In FIG. 1, the x,y, and z directions are defined by the coordinate axes. The numeral 101indicates a dye laser, which emits a laser beam 109, parallel light, ofa wavelength of 700 nm and a beam diameter of about 1 mm. The numeral102 indicates a microlens array module having a 100×100 square latticematrix of microlenses of about 20 μm diameter. Dye laser 101 andmicrolens array 102 are supported by support 107 on fixed table 112. Dyelaser 101 and microlens array module 102 constitute a focused lightarray-forming means. The numeral 103 indicates a glass cell for holdingphotosetting resin 104, a working object, which is to be solidified bypolymerization by application of an exciting energy corresponding to thelight of a wavelength of about 350 nm. The glass cell is set on finex-y-z adjustment mechanism 105. Coarse x-y-z adjustment mechanism 106,having a built-in motor, and fine x-y-z adjustment mechanism 105, havinga built-in PZT element, drive the glass cell 103 coarsely and finely inthe x, y, and z directions and adjust the relative position of glasscell 103 to the focused light array-forming means. Both adjustmentmechanisms are controlled by control device 108 according to theinformation as to the position on support 107. The PZT element enables afine adjustment in a range of several nanometers to several micrometers,and the motor enables a coarse adjustment in the range of severalmicrometers to several millimeters. Support 107, fine x-y-z adjustmentmechanism 105, coarse x-y-z adjustment mechanism 106, and control device108 constitute a drive controlling assembly. FIG. 2 shows theconstitution of drive-controlling assembly 201.

Laser beam 109 is converted to convergent light group 110 by the passagethrough the microlens array. The position of the glass cell 103 isadjusted preliminarily by drive-controlling assembly 201, such that theconvergent light group introduced into photosetting resin 104 formsfocused light array 111 on the interface between photosetting resin 104and the bottom face of glass cell 103, and the laser beam is projectedthereto. Consequently, the photosetting resin is solidified bypolymerization by a two-photon process at and around thelight-concentrating points. In this example, convergent light group 110is projected into the photosetting resin for 5 seconds to form a fineperiodic structure of a two-dimensional matrix having periods of about20 μm in x and y directions and the solidification regions of 200 nm.The diameter of the region of the formed fine period structure is about1 mm corresponding to the laser beam diameter of about 1 mm. After thisprocess, the glass cell is moved by 10 μm in the x direction bydrive-controlling assembly 201, and convergent light group 110 is againprojected. Thereby, a fine periodic structure of a two-dimensionalmatrix having periods of about 10 μm in the x direction and about 20 μmin the y direction and the solidification region of 200 nm is formed.The size of the solidification region can be arbitrarily controlled bycontrolling the convergent light group, the projection time, and otherfactors. In another processing operation, the convergent light group isprojected into photosetting resin 104 with glass cell 103 being driven,immediately after the start of the processing, by drive-controllingassembly 201 in a circular motion of 5 μm diameter in the x-y plane andin a negative z direction. Thereby, a fine periodic structure can beobtained in which solidified regions in a spiral in the z direction arearranged in the x-y plane in the resin. As described above,three-dimensional fine periodic structure can readily be obtained by theprocess for producing a fine periodic structure of the present inventionusing the apparatus structured as described in this Example.

Example 2

FIG. 6 shows a constitution of the fine periodic structure of thepresent invention, employing an optical fiber bundle as the convergentlight array-forming means. The x, y, and z directions are defined by thecoordinate in FIG. 6. The numeral 401 in FIG. 6 indicates the opticalfiber bundle 401 shown as in FIGS. 4 and 5. The optical fiber bundle isheld in optical fiber holder 402 having a hexagonal hole the centralaxes in longitudinal direction of which holder and hole coincide witheach other, and is constituted of sixty-one optical fibers 301 shown inFIG. 3, which are placed in parallel in the hole of the holder andarranged in a triangular lattice in the cross-section perpendicular tothe axis of holder 402. The optical fiber 301 is constituted of fiberportion 302 having a diameter of about 100 μm and a length of about 5cm, and microlens 303. Sixty-one microlenses 303 are placed to have thelens ends uniformly flat at the end face perpendicular to the long axisof holder 402 as shown in FIG. 4 and are arranged in a triangularlattice as shown in FIG. 5. Optical fiber bundle 401 converts laser beam109 to convergent light group 610 emitted from microlenses 303. Convexlens 614 held by lens holder 613 supported by support 107 adjusts thedirections of each of the convergent light beams of convergent lightgroup 610 to decrease the distance between the light-concentratingpoints in light-concentrating point array 612. The direction-adjustedbeams of the convergent light group are emitted from convex lens 614 asmodified convergent light flux 611. Dye laser 101, optical fiber bundle401, and convex lens 614 constitute a focused-light array-forming means.

The position of glass cell 103 is adjusted preliminarily bydrive-controlling assembly 201 such that convergent light group 611introduced into photosetting resin 104 forms focused light array 612 onthe interface between the photosetting resin and the bottom face ofglass cell 103, and the laser beam is projected thereto. For example,projection of focused light group 611 to the photosetting resin for 5seconds forms a two-dimensional fine period structure with a period ofabout 10 μm and a solidified region of about 200 nm. Convex lens 614 iseffective, for example, such that the light-concentrating pointintervals of about 100 μm without convex lens 614 is decreased to about20 μm by use of convex lens 614 and passage of the focused light groupthrough convex lens 614. After this first processing step, the glasscell is moved in the x direction by 10 μm and fixed by drive-controllingassembly 201. Then, convergent light group 611 is projected to thephotosetting resin. Thereby, a two-dimensional fine periodic structureis obtained, which has a period of about 10 μm in the x direction, aperiod of about 20 μm in the y direction, and a solidified region ofabout 200 nm. The size of the solidified region can be variedarbitrarily by adjusting the intensity of the convergent light, theirradiation time, and the like conditions. A fine periodic structurehaving solidified regions in a spiral in the z direction arranged in thex-y plane in the resin can readily be prepared in the same manner as inExample 1. As described above, a three-dimensional periodic structurecan readily be prepared with the apparatus structured as described inthis Example.

Example 3

This example shows a constitution employing a light source and a mask asthe divergent light-generating means. FIG. 10 shows the constitution ofthe apparatus for producing a fine periodic structure employed in thisExample. This apparatus has divergent light-generating means 1002constituted of HeCd laser 101 as the light source for emitting a lightof a wavelength of 355 nm and spot diameter of about 2 mm, and mask 701as the light diverging means. Divergent light group 905 generated bydivergent light-generating means 1002 is introduced into working object104 contained in glass cell 103.

FIG. 7 shows mask 701 employed in this example. This mask 701 is made ofSi substrate 702 of a thickness of about 200 μm in which fine pores 703are bored at intervals of 10 μm in a 3×3 matrix. FIG. 8 is a plan viewof the mask shown in FIG. 7. FIG. 9 is a sectional view taken along line9-9 in FIG. 8. As shown in FIG. 9, parallel light introduced to one faceof mask 701 passes through nine fine pores 703 and is emitted from theother face as nine divergent lights 902 diffracted by the fine pores.The nine divergent lights have spatial overlaps 903,904. The emittedlight beams consisting of these divergent lights are referred to as adivergent light group.

As working object 104, an epoxy type photosetting resin is used, whichhas an absorption band region in the wavelength region longer than thewavelength of an HeCd laser for polymerization.

Laser light beam 1003 emitted from HeCd laser 101 is directed to oneface of mask 701, and divergent light group 905 is allowed to be emittedfrom the other face. This divergent light group 905 is introduced intophotosetting resin 104. The beams of divergent light group 905, whichhave the same wavelength and three-dimensional overlap, interfere inphotosetting resin 104 to form an interference pattern in the lightintensity distribution. In the photosetting resin, portions where thelight energy intensity is not lower than that for initiation of thepolymerization are cured, and the rest of the resin remains uncured in aliquid state. Removal of the remaining liquid resin by washing yields afine periodic structure formed from cured photosetting resin 104corresponding to the light intensity distribution.

In this example, for producing a three-dimensional structure, two HeCdlasers 1006 for a wavelength of 355 nm are placed at the lateral sidesof glass cell 103 in an opposed arrangement, as shown in FIG. 10. Lightbeams 1007 of 2 mm in spot diameter emitted from HeCd lasers 1006 areexpanded by beam expanders 1008 to beams 1009 of spot diameters of about2 cm. Beams 1009 are projected into photosetting resin 104 in paralleland in an opposite direction to each and interfere with each other toform a standing wave in a one-dimensional direction in the resin.Similar to divergent light group 905, portions of the resin are curedwhere the light energy intensity is not lower than that for theinitiation of the polymerization, and the rest of the resin remainsuncured in a liquid state. Removal of the remaining liquid resin bywashing yields a fine periodic structure constituted of curedphotosetting resin 104 corresponding to the light intensitydistribution.

A three-dimensional fine periodic structure can be produced in a shortperiod of time with a high level of precision using the apparatus havinga structure as described in this Example.

Example 4

In this example, the divergent light-generating means is comprised of alight source and an optical fiber bundle comprising at least one opticalfiber having a fine lens at the end thereof.

FIG. 11 shows the introduction of incident light beam 1105 into fiberbundle 1102 of this Example constituted of nine optical fibers 1103 heldby fiber holder 1101. Microlenses 1107 are provided at the ends of theoptical fibers 1103 at the divergent light emission side. The opticalfibers have a diameter of 50 μm and have a microlens formed by fusion ofthe tip by laser irradiation at the respective ends. Fiber holder 1101is made of an Si substrate, having fine pores in a two-dimensionalperiodic arrangement formed by photolithography for setting the opticalfibers.

FIG. 12 shows an apparatus for producing a fine periodic structureemploying a divergent light-generating means comprised of a light sourceand optical fiber bundle 1102 shown in FIG. 11. The numerals 1201, 1202,and 1203 indicate, respectively, a laser for emitting ultraviolet lightof 320, 340, or 360 nm. The three lasers are connected respectively tothree of optical fibers 1103 by fiber couplers 1204. Laser beams areintroduced to the optical fibers, and divergent light groups 1213emitted from microlenses 1107 are introduced to photosetting resin 104,a working object, contained in glass cell 103. The numeral 1212indicates a base of the apparatus. Fiber holder 1101 is supported by afiber holder-supporting portion of base 1212. Optical fibers 1103 areconnected to optical switches 1205. The light passing through opticalfiber 1103 can be switched by controlling the optical switches byoptical switch driving device 1211 through wiring 1210.

In this example, plural wavelengths of the light beams are employed forintroducing light into the respective optical fibers, whereby theinterference configuration formed by divergent light beams emitted frommicrolenses 1107, namely the light intensity distribution, is made to bedifferent from the interference configuration obtained from singlewavelength light.

This application claims priority from Japanese Patent Application No.2003-344412 filed on Oct. 2, 2003, which is hereby herein incorporatedby reference.

1. A process for producing a periodic structure, comprising the stepsof: preparing a working object which changes a property thereof byphotoreaction caused by an exciting energy; generating a light having aphotonic energy of intensity of one fraction of natural number divisionsof the exciting energy by each of light sources of light-source groupsarranged regularly in two-dimensional arrangement; and concentrating thelight emitted from light source group at each of light-concentratingpoints arranged at regular intervals in the working object to causephotoreaction at and around the light-concentrating point to form aperiodic structure comprised of regions each of which has a changedproperty in the working object.
 2. The process for producing a periodicstructure according to claim 1, wherein the photoreaction is amultiphoton absorption reaction.
 3. The process for producing a periodicstructure according to claim 1, wherein the lights from the light sourcegroup are introduced through a light-condensing optical system to theworking object.
 4. The process for producing a periodic structureaccording to claim 1, wherein the lights from the light source group arecoherent lights, and the lights from the light source group areinterfered with each other in the working object, to make the lightsconcentrated.
 5. The process for producing a periodic structureaccording to claim 1, wherein the lights from the light source group aregenerated by a single light-generating source.
 6. The process forproducing a periodic structure according to claim 1, wherein the lightsource group is comprised of a single light-generating source and a maskhaving fine pores arranged periodically in one plane, and the light fromthe light-generating source is introduced to one face of the mask andemitted from the other face thereof.
 7. The process for producing aperiodic structure according to claim 1, wherein the light source groupis comprised of a single light-generating source and a microlens arraycomprising microlenses arranged periodically in one plane, and the lightfrom the light-generating source is introduced to one face of themicrolens array and emitted from the other face thereof.
 8. The processfor producing a periodic structure according to claim 1, wherein thelight source group is comprised of a single light-generating source andan optical fiber bundle of optical fibers bundled regularly each ofwhich fibers has a microlens on one end, and the light from thelight-generating source is introduced to an end of the optical fiberbundle having no microlens, and emitted from the other end of the fiberbundle.
 9. The process for producing a periodic structure accordingclaim 1, wherein the periodic structure is formed in three dimensions bychanging the relative position of the light-concentrating points and theworking object.